The present invention relates to a rolling bearing suitable for use as a bearing for, for example, a swing arm which is provided in a magnetic disk apparatus and swings minutely at a high speed.
A swing arm for a magnetic disk apparatus is required to swing minutely at a high speed in order that a magnetic head disposed at the leading end of the swing arm is able to seek a target track on a magnetic disk at a high speed and with high accuracy. To realize such high-speed and minute swing motion, there is used a rolling bearing in the base end swing portion of the swing arm. FIG. 9 is a section view of a swing arm base end which is supported by a conventional rolling bearing. On the inside portion of a casing 1 for an actuator (for example, a voice coil motor) which carries out a high-speed and minute swinging motion, there is threadedly mounted a base plate 3; and, the lower end of a support shaft 5 is fitted with and fixed to one end of the base plate 3. Also, the upper end of the support shaft 5 is threadedly mounted on the casing 1 by a screw 6 which extends through the casing 1.
On the outer periphery of the support shaft 5, there are disposed a pair of ball bearings (rolling bearings) 7 in such a manner that they are spaced apart from each other in the axial direction of the support shaft 5. Each of the ball bearing 7 is disposed in such a manner that its inner race is fixed to the support shaft 5 and its outer race is fixed to a housing 9. To the outer periphery of the housing 9, there is fixed the base end of a swing arm 11, while the swing arm 11 is swingably supported on the support shaft 5 through the ball bearings 7. At the leading end of the swing arm 11, there is disposed a magnetic head (not shown). Also, on the outer periphery of the housing 9, there is disposed a voice coil portion 13, while the voice coil portion 13 is situated in a magnetic field which is formed by two permanent magnets 15 disposed within the housing 9. Accordingly, in case where a given current is caused to flow in the voice coil portion 13 by a magnetic circuit, there is applied a rotational force to thereby swing the swing arm 11 by a given amount.
By the way, into the ball bearing 7 of this type, there is enclosed lubricant such as lubricating oil or grease for the purpose of lubrication. Conventionally, the amount of enclosure of the lubricant into the ball bearing is generally set in the range of 10 to 20% of the capacity of a space formed in the inside portion of the ball bearing.
Also, conventionally, the two ball bearings 7, 7, into which grease is enclosed as lubricant, are respectively given a pre-load (that is, an axial load applied to a bearing to thereby adjust a clearance between a rolling element and inner and outer races in order to prevent the shaft of the bearing from swinging as well as prevent the rolling element from slipping, swinging and generating noises) before they are put into practical use. And, as shown in FIG. 10, adhesives are applied to the peripheries of inner race inside diameter surfaces 7a, 7a and outer race outside diameter surface 7b, 7b, so that the two ball bearings 7, 7 can be bonded and fixed to the support shaft 5 and housing 9. Also, the both side surfaces of each of the ball bearings 7, 7 can be normally sealed through seal members 73. By the way, conventionally, the pre-load is generally set in the range of 300 gf to 800 gf.
In recent years, as the magnetic disk apparatus becomes highly dense, the magnetic disk apparatus is required that a spacing between the magnetic head and magnetic disk is as narrow as possible. Due to this, for the reliability of the magnetic disk apparatus, control of contamination becomes more and more important. Especially, since the swing arm is disposed adjacent to the magnetic disk surface, the swing arm is required that it is as free as possible from the contamination. For this reason, for the ball bearing, there are needed lubricant and lubricating method which can reduce the evaporation and scattering of the lubricant further than the conventional lubricant and lubricating method.
On the other hand, the track width of the magnetic disk has been made narrower and narrower, which requires the swing arm to speed up its access to the target track and enhance the accuracy of its positioning operation. This in turn requires the ball bearing, which supports the swing arm, that it can prevent an increase in torque as well as a sudden variation in the torque (torque spike).
However, the conventional ball bearing for a swing arm generally aims at extending its life and enclosing thereinto a large amount of grease in the range of 10 to 20% of the capacity of the space formed in the inside portion of the ball bearing. Therefore, in the conventional ball bearing, there are necessary various devices to eliminate a fear that outgases can be generated due to the evaporated or scattered grease, and a fear that such outgases can stick to the surface of the magnetic disk. Also, in case where the grease enclosure amount is increased for enhancement of the durability of the bearing, the viscosity and mixing resistance of the grease increase to thereby cause the torque to vary and increase.
The present invention aims at eliminating the drawbacks found in the conventional rolling bearings. Accordingly, it is an object of the invention to provide a rolling bearing which, while preventing fretting wear occurring when lubricant is small in amount, can keep torque from increasing or varying and can prevent contaminations from being produced due to the evaporation and scattering of the lubricant.
In attaining the above object, according a first aspect of the invention, there is provided a rolling bearing structured such that, in the inner peripheral surface of an outer race and the outer peripheral surface of an inner race, there are formed raceway surfaces respectively and, between these raceway surfaces, there are interposed a plurality of rolling elements, whereby the inner and outer races are assembled to each other through the rolling elements, wherein, in a space formed between the raceways of the outer and inner races, there is enclosed lubricant in an amount of 0.3% to 3% of the capacity of the space.
In the present rolling bearing, in the space formed between the raceways of the outer and inner races, there is enclosed the lubricant and the lubricant enclosure amount is set in the range of 0.3-3% of the capacity of the space. Due to this, there can be secured a proper amount of lubricant. The proper amount of w lubricant can prevent not only the early fretting wear of the bearing surfaces as well as the damage of raceway surfaces and rolling elements which are easy to occur in case of the lubricant enclosure amount of less than 0.3%, but also the evaporation and scattering of the lubricant as well as the increase and variation in the torque which are easy to occur in case of the lubricant enclosure amount of more than 3%. Therefore, in case where a rolling bearing according to the invention is used as a bearing for a swing arm provided in a magnetic disk apparatus, the high-speed and high-accuracy operation of the swing arm can be realized with reduced contaminations.
Also, according to a second aspect of the invention, there is provided a rolling bearing, wherein a seal member for closing an annular clearance of the above-mentioned space opened on the two end faces of the above-mentioned outer and inner races may be fixed to either of the outer race or inner race.
In the present rolling bearing, the annular clearance of the above-mentioned space opened on the two end faces of the outer and inner races is sealed by the seal member, thereby being able not only to prevent foreign objects from invading the inside portion of the bearing from outside but also to prevent the lubricant enclosed in the space from evaporating and scattering to the outside. This not only can extend the life of the rolling bearing but also can reduce the contaminations that are involved with the evaporation and scattering of the lubricant.
In achieving the above object, according to a third aspect of the invention, there is provided a rolling bearing structured such that, in the inner peripheral surface of an outer race and the outer peripheral surface of an inner race, there are formed raceway surfaces respectively and, between these raceway surfaces, there are interposed a plurality of rolling elements, whereby the inner and outer races are assembled to each other through the rolling elements, wherein, at least on the raceway surfaces of the outer and inner races and the surfaces of the rolling elements, there is formed a coating or a thin film obtained by diluting and vacuum drying oil.
In the present rolling bearing, the coating or thin film obtained by diluting and vacuum drying oil is formed on the raceway surfaces and the surfaces of the rolling elements, which can reduce the evaporation and scattering of the lubricant as well as can reduce the viscosity and mixing resistance of the lubricant to a great extent to thereby prevent the torque from increasing or varying, when compared with the conventional rolling bearing in which lubricating oil or grease is enclosed. Therefore, in case where a rolling bearing according to the invention is used as a bearing for a swing arm provided in a magnetic disk apparatus, the high-speed and high-accuracy operation of the swing arm can be realized with reduced contamination.
Also, according a fourth aspect of the invention, there is provided a rolling bearing, wherein a seal member for closing an annular clearance of the above-mentioned space opened on the two end faces of the above-mentioned outer and inner races may be fixed to either of the outer race or inner race.
In the present rolling bearing, the annular clearance of the above-mentioned space opened on the two end faces of the outer and inner races is sealed by the seal member, thereby being able not only to prevent foreign objects from invading the inside portion of the bearing from outside but also to prevent the lubricant enclosed in the space from evaporating and scattering to the outside. This not only can extend the life of the rolling bearing but also can reduce the contaminations that are involved with the evaporation and scattering of the lubricant.
Further, according to a fifth aspect of the invention, there is provided a method for forming a lubricating oil film for a rolling bearing which is structured such that an inner race is disposed on the inner periphery of an outer race, there are raceway surfaces respectively on the inner peripheral surface of the outer race and on the outer peripheral surface of the inner race, there are interposed a plurality of rolling elements between these raceway surfaces, and the inner and outer races are free to rotate with respect to each other through the rolling elements, the method comprising the steps of: pouring a previously diluted lubricating oil onto the raceway surfaces and the surfaces of the rolling elements; rotating the inner and outer races with respect to each other to thereby apply the lubricating oil onto the raceway surfaces and the surfaces of the rolling elements; and, vacuum drying the rolling bearing with the lubricating oil applied thereon to thereby form a coating or a thin film on the raceway surfaces and the surfaces of the rolling elements.
According to the present rolling bearing lubricating oil film forming method, after the diluted lubricating oil is poured, it is dried. Due to this, a step of pouring a very small amount of lubricating oil can be realized easily. Also, by vacuum drying the lubricating oil, when compared with a method in which lubricating oil is thermally treated, the coating or thin film can be formed at an inexpensive manufacturing cost.
According to a sixth aspect of the invention, there is provided a rolling bearing, wherein diluted oil is vacuum dried to thereby form a coating or a thin film at least on the raceway surfaces and sliding surfaces of the bearing surfaces, and a seal member or a shield member (a sealing plate) serving as a sealing device is not provided on the side surfaces of said rolling bearing to thereby provide the rolling bearing as an open product. In particular, according to the present aspect of the invention, there is provided a rolling bearing for a swing arm, wherein diluted and vacuum dried oil is used to form a coating or a thin film at least on the raceway surfaces and sliding surfaces of the bearing surfaces. That is, the present invention relates to a structure for coating lubricating oil on the raceway surfaces with which balls serving as rolling elements can be contacted. The portions that can be contacted by the balls serving as the rolling elements are the raceway surfaces and the sliding surfaces of the pocket surfaces of retainers; and thus, the present invention relates to a structure for coating the lubricating oil onto these surfaces. Therefore, the present structure can be applied not only to the ball bearing but also to a roller bearing which uses rollers as rolling elements.
According to a seventh aspect of the invention, there is provided a rolling bearing, wherein lubricating oil (fluorine-containing oil or ester-containing oil) is diluted with a highly volatile alternative Freon, is poured onto the raceway surfaces of the inner and outer races of the rolling bearing and is dried at a temperature of the order of 80 to 120xc2x0 C. under vacuum conditions for about 0.5 to 3 hours; after then, the inner and outer races are respectively pressure inserted into and fixed to a support shaft and a housing according to a resonance pressure insertion method; and, due to the rotation of the rolling bearing, there is formed a coating not only on the raceway surfaces of the inner and outer races serving as the contact surfaces of the inner and outer races but also on sliding surfaces which are the contact surfaces of the pocket surfaces of the retainers with rolling elements, while the enclosure amount of the lubricating oil is set in the range of 0.3 to 3% of the capacity of a space formed in the inside portion of the rolling bearing.
According to the present invention, in case where the diluted oil (lubricating oil) is vacuum dried to thereby form a coating or a thin film on, of the bearing surfaces, at least the raceway surfaces and sliding surfaces, the evaporation and scattering of the lubricant can be reduced when compared with the conventional rolling bearing in which grease is used as lubricant. Also, since the oil is easy to enter the contact surfaces which are moving and is excellent in oil film forming property and in repairing property, the level of torque can be reduced as well as variations in the torque can be reduced.
Further, in case where a seal plate or a shield plate serving as a sealing device is not provided on the side surfaces of the bearing to thereby form the bearing as an open product, the bearing can be cleaned in a state where it is assembled into a unit and in a state where the unit is mounted on a swing arm. That is, due to removal of the sealing device which has been conventionally an obstacle to cleaning, the cleaning of the bearing in a state where it is assembled into a unit and in a state where the unit is mounted on a swing arm can be facilitated, resulting in the positive cleaning (enhanced purity) of the bearing. Thanks to this, after the bearing is assembled, a final cleaning operation can be enforced on the bearing to thereby enhance the purity thereof. Also, since the number of steps of cleaning the bearing in the bearing assembling process can be reduced, the manufacturing cost of the bearing can be decreased.
According to a seventh aspect of the invention, there is provided a rolling bearing apparatus, comprising:
an inner race portion for supporting a rolling element from inside of the center of rotation in a freely rollable manner;
an outer race portion for supporting a rolling element from outside of the center of rotation in a freely rollable manner; and,
a rolling element interposed between said inner and outer race portions,
wherein oil is used as lubricant applied between the inner and outer race portions and the rolling element, and a pre-load to be applied to the rolling bearing apparatus is set in the range of 50 to 200 gf.
In the present rolling bearing apparatus, since oil is used as the lubricant and the pre-load is set in the range of 50 to 200 gf, not only the structure of the rolling bearing apparatus can be made simple and inexpensive, but also the level of torque can be decreased and control on variations in the torque can be promoted while reducing the evaporation and scattering of the lubricant, when compared with the conventional rolling bearing apparatus in which grease is used as lubricant and a pre-load is set in the conventional range.
That is, while restricting the deterioration of the bearing apparatus caused by use of the oil as the lubricant as much as possible, the torque level can be decreased and torque variation control can be promoted, which makes it possible to speed up the position control of the bearing apparatus as well as enhance the accuracy thereof. Thanks to this, there can be provided a rolling bearing apparatus suitable for use in a portion which swings minutely at a high speed, and thus there can be provided a rolling bearing apparatus suitable for use in a high-performance swing arm.